fix: remote python sdk namespace typing (#2620)

This changes the default values for some namespace parameters in the
remote python SDK from None to [], to match the underlying code it
calls.

Prior to this commit, failing to supply "namespace" with the remote SDK
would cause an error because the underlying code it dispatches to does
not consider None to be valid input.

python/python/tests/test_db.py

@@ -175,6 +175,18 @@ def test_table_names(tmp_db: lancedb.DBConnection):
     tmp_db.create_table("test3", data=data)
     assert tmp_db.table_names() == ["test1", "test2", "test3"]
 
+    # Test that positional arguments for page_token and limit
+    result = list(tmp_db.table_names("test1", 1))  # page_token="test1", limit=1
+    assert result == ["test2"], f"Expected ['test2'], got {result}"
+
+    # Test mixed positional and keyword arguments
+    result = list(tmp_db.table_names("test2", limit=2))
+    assert result == ["test3"], f"Expected ['test3'], got {result}"
+
+    # Test that namespace parameter can be passed as keyword
+    result = list(tmp_db.table_names(namespace=[]))
+    assert len(result) == 3
+
 
 @pytest.mark.asyncio
 async def test_table_names_async(tmp_path):